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The article presents a quantitative estimation of dust source contributions to the Chinese Loess Plateau (CLP), based on more than 37,100 detrital zircon U-Pb ages, combined with mineral assemblages and isotope analyses. Topics discussed include detrital zircon age spectra and the potential dust sources, quantitative estimation of the contributions from different sources, and temporal variations in the provenance of the CLP.

The Cenozoic erosion history of the Himalaya-Karakoram, which is a function of tectonically driven uplift and monsoon climatic evolution in South Asia, remains elusive, especially prior to the Miocene. Here, we present a multiproxy geochemical and thermochronological analysis of the oldest samples available from the Arabian Sea, which we used to investigate the erosion history of the Himalayan and Karakoram orogenic system. The Indus Fan records rapid and sustained erosion of the Himalayan-Karakoram mountains from before 24 Ma (ca. 30) to ca. 16 Ma concurrent with changing provenance from the Indian (Himalayan) and Eurasian plates. Our data, combined with previous studies of younger Indus Fan deposits, indicate that the mid-to-late Cenozoic erosion history of the Himalayan-Karakoram mountains is overall consistent with a vigorous monsoonal climate from the late Oligocene to middle Miocene and with changes in global climate in the late Miocene, whereas erosion and deposition are relatively insensitive to changes in sources and rock erodibility. Although tectonic processes were active throughout, we suggest that the erosional signatures of the Himalayan-Karakoram mountains from the Indus Fan largely preserve a record of climate changes since the Oligocene. [ABSTRACT FROM AUTHOR]

The article highlights the role of high- and low-latitude forcing of East Asian monsoon variations on tectonic and orbital time scales. It mentions information about the high-resolution precipitation record from Pliocene fluvial-lacustrine sequences in the Weihe Basin, Central China, a region sensitive to the East Asian monsoon.

The Luonan Basin, located in the transitional zone between temperate and subtropical China, is an important locality for human evolution during the early to middle Pleistocene. The loess deposits in the Luonan Basin contain numerous in situ lithic artefacts; the deposits also constitute suitable material for dating the artefacts and are potentially useful for reconstructing the climatic fluctuations which is important for studying the adaptation and occupation of the area by early humans. We carried out a combined rock magnetic and geochemical investigation of a loess sequence from the Liuwan Palaeolithic site in the Luonan Basin. The results indicate a mixture of magnetic minerals, including magnetite/maghemite and hematite/goethite. Magnetic susceptibility was used as a palaeoclimate proxy on the Chinese Loess Plateau; however, its application to the Luonan Basin may be problematic because the provenance of the loess parent material, as well as the depositional environment, differs from that of the Chinese Loess Plateau. We found that rock magnetic parameters related to the grain size of magnetic minerals, such as SIRM/χ and χARM/SIRM, are better palaeoclimatic indicators than magnetic susceptibility. Overall, the magnetic results, together with the results of bulk grain-size and chemical index of alteration, indicate that the interglacial environment of early humans in Luonan Basin was warmer and more humid than the coeval environment of the Chinese Loess Plateau. [ABSTRACT FROM AUTHOR]

Paleoclimatic research can provide critical insight on causes of change in the East Asian monsoon, which influences the lives of 1.6 billion people today. In this study, we use paleoclimatic indexes from Chinese loess deposits, which have clear climatic implications and are independently dated, to reconstruct the monsoon precipitation since 21 ka. Our results show that monsoon precipitation persistently decreased from 21 ka to ca. 8 ka, and increased after ca. 8 ka, with a precipitation peak at 8-3 ka. These changes in East Asian summer monsoon precipitation are synchronous with changes in high-northern-latitude ice volume/ice cover and atmospheric CO2. These new data suggest that variation of the monsoon precipitation was probably driven by CO2-forced high-northern-latitude temperature changes, shifting the location of the intertropical convergence zone that dominates monsoon precipitation. Our TraCE-21000 modeling experiment supports this interpretation. [ABSTRACT FROM AUTHOR]

Previous palaeoclimatic studies in the northeastern Qinghai-Tibetan Plateau (NETP) during the Holocene, mainly using lake sediments, have deepened our understanding of the climatic system in this remote region. The timing and forcing mechanisms of climatic change in this region are still controversial, however. Aeolian sand and silt deposits, which are widely distributed in the NETP, can be readily dated by optically stimulated luminescence (OSL) techniques and reveal the sensitive response of the landscape to climatic change. In this study, aeolian sand and loess at six sites around Qinghai Lake were studied to reconstruct millennial-scale climatic changes during the Holocene. Multiproxy data along with 24 OSL age determinations show that low effective moisture and aeolian activity occurred at c. 13 ka, 10—9.1 ka, and 8.9—7.8 ka. Periods of greater effective moisture may have occurred at ~11 ka and 9 ka, and there is evidence for a previously undocumented wet climate at 4—3 ka. These results show that millennial-scale Holocene palaeoclimatic changes in the NETP cannot be explained simply as direct responses to changes in monsoon precipitation forced by summer insolation. We suggest that changes in effective moisture were determined by the balance between monsoon-induced rainfall and evaporation loss (mainly controlled by temperature). Thus, climatic change in the NETP may have been influenced by complex interactions between the monsoon circulation and local convection/evaporation effects, in addition to large-scale change in the Asian monsoon and the westerlies. [ABSTRACT FROM AUTHOR]

Understanding loess sedimentation rates is crucial for constraining past atmospheric dust dynamics, regional climatic change and local depositional environments. However, the derivation of loess sedimentation rates is complicated by the lack of available methods for independent calculation; this limits interpretation of the environmental changes revealed by the loess record. In particular, while the Quaternary/Neogene Chinese loess and Red Clay sequences have the potential to provide detailed records of past sedimentation and climate change, there is great uncertainty concerning: (i) the influences on sediment grain-size and accumulation; and (ii) their relationship through time and across the depositional region. This uncertainty has led to the widespread use of assumptions concerning the relationship between sedimentation rate and grain-size in order to derive age models and climate reconstructions. To address this uncertainty, detailed independent age models, based on optically stimulated luminescence dating, undertaken at 10 to 40 cm intervals at five sections across the Loess Plateau in China, have been used to calculate sedimentation rates and make comparisons with grain-size changes over the late Pleistocene and Holocene. The results demonstrate that sedimentation rates are site specific, extremely variable over millennial timescales and that this variation is often not reflected in grain-size changes. In the central part of the Loess Plateau, the relationship between grain-size and sedimentation rate appears most complex, suggesting an interplay between local conditions at source and sink and a changing emplacement mechanism. This observation further undermines the common use of loess sedimentation age models that rely on a derived relationship between grain-size and sedimentation rate from a type section. The results also highlight the difficulty in assigning specific environmental causes to sedimentation rate changes and, to a lesser extent, grain-size shifts. [ABSTRACT FROM AUTHOR]

Chinese loess is regarded as one of the most detailed and complete terrestrial archives of late Cenozoic climate change. However, high-resolution optically stimulated luminescence (OSL) dates presented here reveal that the suborbital chronological framework of Chinese loess used in many previous climate reconstructions requires reassessment. Chronological uncertainty of as much as 10-15 k.y. for the late Pleistocene is largely a result of the widespread use of nonradiometric dating techniques that fail to account for site-specific depositional conditions associated with loess emplacement and diagenesis. OSL-based age models that account for these processes are used to examine detailed records of past sedimentation, as well as grain size and magnetic susceptibility proxies for late Pleistocene East Asian monsoon variation. Abrupt shifts in monsoon proxies occur over 102-103 yr time scales, potentially forced by a variety of factors and influenced by site location and site-specifi c changes in sedimentation. [ABSTRACT FROM AUTHOR]

The loess–palaeosol deposit on the northeastern Qinghai-Tibetan Plateau is sensitive to environmental changes, thus providing a good opportunity to investigate regional palaeoenvironmental evolution and its relationship with global climatic changes. Detailed rock magnetic investigations and grain-size determination were carried out on a 35-m-thick loess–palaeosol sequence at Dongchuan, the northeastern Qinghai-Tibetan Plateau. The principal ferrimagnetic minerals in both the loess and palaeosol units are large pseudo-single domain magnetite/maghemite. Palaeosol units are generally enriched in ultrafine-grained magnetite/maghemite of pedogenic origin. Variations of low-field magnetic susceptibility and frequency-dependent susceptibility in the loess and palaeosols can mainly be attributed to changes in the concentration of these minerals. Higher values of frequency-dependent susceptibility occur in the palaeosol horizons except for the weakly developed palaeosol, suggesting that higher concentrations of ultrafine magnetite/maghemite particles occur in palaeosol units due to in situ pedogenesis. The frequency-dependent susceptibility of the loess units is very low and uniform, indicating absence of the super-paramagnetic grains and negligible pedogenically induced enhancement of magnetic susceptibility. Generally, magnetic susceptibility combined with the frequency-dependent susceptibility of the loess–palaeosol sequences reflect the glacial-interglacial changes, thus can be employed as a proxy measure of palaeoclimate in this region. However, the low-field magnetic susceptibility record does not consistently correlate to the variations in stratigraphy of the Dongchuan loess–palaeosol sequence. It is thus suggested that multiparameter rock magnetic investigations combined with non-magnetic measurements, such as grain-size analysis, represent a more powerful approach for palaeoclimatic research into the complex loess–palaeosol record in the Qinghai-Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Recent chronological studies have revealed significant site-specific variations in loess sedimentation, which challenge the use of loess deposits as continuous, easily analyzable paleoclimate and dust records. However, the regional comparability of loess sedimentation at subglacial-interglacial time scales has not yet been systematically tested. This study focused on the spatial and temporal variability of loess sedimentation on the Chinese Loess Plateau (CLP) during the last 20 thousand years and found a clear seesaw pattern across the CLP, indicated by rapid dust accumulation at the desert margin and reduced accumulation/less preservation on the main part of the CLP after ca. 15 ka. This spatial inhomogeneity of loess sedimentation at millennial time scales is controlled by various dust transportation, trapping, and postdepositional processes in different geographic settings, which are ultimately attributed to a combined effect of a weakened winter monsoon and enhanced summer monsoon after the termination of Heinrich event 1. [ABSTRACT FROM AUTHOR]

The Xiashu loess is a typical Quaternary eolian deposit in southern China and represents an important terrestrial paleoclimate archive in this low-latitude monsoon region. However, the chronological framework of Xiashu loess deposition has yet to be established. Determining the timing of the onset of Xiashu loess deposition will allow researchers to better understand late Quaternary aridification across the Asian continent, the evolution of the East Asian monsoon and regional environmental changes in subtropical regions. Therefore, in this study, a systematic chronological study of the Xiashu loess is conducted to answer this question. For the first time, magnetostratigraphic classification reveals that the Matuyama/Brunhes (M/B) reversal is present in the Xiashu loess at two sites in Jiangsu Province, the Qingshan profile at Yizheng and the Dagang core in Zhenjiang. Based on the results of magnetostratigraphy and optically stimulated luminescence (OSL) dating, the age of the lower boundary of the Xiashu loess is estimated to be approximately 0.9 Ma. Consequently, this Xiashu loess deposit is the oldest reported to date and is comparable in age to the red soil deposit in Xuancheng, Anhui Province. The onset of Xiashu loess deposition by 0.9 Ma represents the further expansion of arid range in Asia in the late Quaternary in response to significant aridification and winter monsoon strengthening in this subtropical region. We suggest that these climate changes were primarily driven by global cooling and an increase in high-latitude ice volume in the Northern Hemisphere and that the initiation of Xiashu loess accumulation was a regional response of southern China to the 0.9 Ma global cooling event. [ABSTRACT FROM AUTHOR]

Geomorphologically, alluvial deposits in river systems are expected to be older on higher terraces than on the lower terraces. However, loess deposits of aeolian origin may also occur on the surface of terrace systems and as seen in the Chinese Loess Plateau (CLP). Such loess is continuously, rather than episodically deposited. This study presents numerous dating results of loess cover on the Hanjiang River terrace system in the southern Qinling Mountains, an atypical loess deposit belt outside of the CLP. We name this "Hanjiang Loess". Results indicate that the Hanjiang Loess deposited on the high, middle, and low terraces are also the oldest, old, and most recent, respectively, apparently analogous with alluvial expectations. Wethus propose a modified depositional hypothesis, whereby terrace loess reflects the deposition of aeolian loess and other material, subsequent fluvial reworking. This depositional hypothesis should also be applicable to loess deposits on the river terraces in the Xiashu Loess, Quaternary Reticulate Red Clay, and Quaternary Red Clay in southern China, and other atypical loess areas outside of the CLP. [ABSTRACT FROM AUTHOR]

Chinese loess has been extensively utilized to produce continuous and high-resolution climate records of the late Cenozoic. Such work assumes uninterrupted loess deposition and limited diagenesis. Here, closely spaced optically stimulated luminescence (OSL) dates are used to characterize the Hobocene and Late Pleistocene sedimentation histories of three sites across a NW-SE transect of the Chinese Loess Plateau. The results suggest that sedimentation is episodic at subglacial-interglacial time scales, with rates rapidly varying within units and between sites. Unconformities, noneolian deposition, and mixing of sediments also appear to be common. Existing understanding of loess deposition therefore requires reexamination, while previous reconstructions of rapid climate change, not dated using absolute methods, should be regarded with caution. Loess deposits may still yield detailed climate records from specific high-sedimentation-rate strata, and evidence for rapid climate change may yet be obtainable by targeting these units through absolute dating. The rapid changes in sedimentation presented here indicate the East Asian Monsoon has the capacity to vary on millennial scales. [ABSTRACT FROM AUTHOR]

River aggradation or incision at different spatial-temporal scales are governed by tectonics, climate change and surface processes which all adjust the ratio of sediment load to transport capacity of a channel. But how the river responds to differential tectonic and extreme climate events in a catchment is still poorly understood. Here, we address this issue by reconstructing the distribution, ages and sedimentary process of fluvial terraces in a tectonically active area and monsoonal environment in the headwaters of the Yangtze River in the eastern Tibet Plateau. Field observations, topographic analyses and optically stimulated luminescence (OSL) dating reveal a remarkable fluvial aggradation, followed by terraces formations at elevations of 62-55 m (T7), 42-46 m (T6), 38 m (T5), 22-36 m (T4), 18 m (T3), 11 m (T2), 2-6 m (T1) above the present floodplain. Gravelly fluvial accumulation more than 62 m thick has been dated prior to 24-19 ka. It is regarded as a response to cold climate during the Last Glacial Maximum. Subsequently, the strong monsoon precipitation contributed to cycles of rapid incision and lateral erosion, expressed as cut-in-fill terraces. The correlation of terraces suggests that specific tectonic activity controls the spatial scale and geomorphic characteristics of the terraces, while climate fluctuations determine the valley filling, river incision and terrace formation. Debris and colluvial sediments are frequently interbedded in fluvial sediment sequences, illustrating the episodic short-time blocking of the channel around 20 ka. This indicates the potential impact of extreme events on the geomorphic evolution in the rugged terrain. [ABSTRACT FROM AUTHOR]

Abstract Reconstructing dust Mass Accumulation Rate (MAR) from loess deposits is critical to understanding past atmospheric mineral dust activity and requires accurate independent age models from loess deposits across Europe and Asia. Previous correlations of loess in Europe and China have tended to focus on multi-millennial timescales, with no detailed examination of dust MAR at the two ends of the Eurasian loess belt on shorter, sub-orbital scales. Here we present a detailed quartz optically stimulated luminescence (OSL) chronology from the Serbian Titel Loess Plateau (Veliki Surduk loess core) and the Chinese Loess Plateau (Lingtai section). The luminescence ages pass internal tests and show consistent increases in age with depth, with no obvious major hiatuses. However, as reported before, it seems the quartz OSL technique is only capable of accurate age determination up to accrued doses of ca. 150 Gy (ca. 30–40 ka) due to approaching field saturation of the quartz OSL signal. Two age-depth models were used to reconstruct dust MARs, where one utilises OSL data solely and the other additionally makes assumptions about sedimentation rates. Although short-term fluctuations in MAR are model dependent, general MAR patterns between the two sites are very similar, with peak MAR occurring rather late in the last glacial (ca. 13–25 ka). This suggests that at least broad scale trends in dust activity within the last glacial period may be similar at a continental scale. [ABSTRACT FROM AUTHOR]

The Qinling Mountains (QLM) in Central China with numerous Paleolithic localities is an important area for hominin occupation and settlement during the early to middle Pleistocene. Paleolithic archaeological survey was carried out in the Lushi Basin in the middle of South Luohe River, central China, Hundreds of paleolithic artifacts were collected and in situ lithic artifacts have been found buried in loess deposits. To establish the reliably chronological framework of the loess sediments and find the age of human occupation, luminescence dating is investigated to obtain age controls. Preliminary dating results using quartz SAR-OSL, TT-OSL and feldspar pIRIR290 show that the samples are beyond the age limitation because of signal saturation. Here we investigated the post-blue violet stimulated luminescence (VSL) using a single aliquot regenerative dose (SAR) protocol and a multiple aliquot additive dose (MAAD) protocol. The SAR VSL signal are not saturated but have 2D0 values < 800 Gy, indicating underestimated Des compared to the 2D0 values of saturated quartz TT-OSL and feldspar pIRIR290 signals. The original VSL decay curve can separate into two components with distinct bleaching characteristics. Under violet laser bleaching, component A, derived from early signal integration, have a lifetime of 66 s, whereas component B, derived from later signal integration, have a lifetime of 281 s. Under sunlight bleaching, component A and B have lifetime of 7.2 hours and 18.3 hours, respectively. Then component A signals were selected to establish the dose response curve (DRC) and determine the Des using MAAD protocol. The established DRCs have 2D0 values >2500 Gy and equivalent dose of a Luochuan S1 layer loess sample (~120 ka) was successfully determined. Based on our resultant luminescence ages, the Lushi Basin loess samples are buried between ~400-700 ka which are in agreement with the pedostratigraphic and magnetic susceptibility correlation with the well-dated loessepaleosol sequences of the North Qinling Mountain and central Chinese Loess Plateau. Our VSL ages in combination with magnetostratigraphic analyses and pedostratigraphic analysis suggest that the the Paleolithic layer dates back to ~1500 ka, offering a poential understanding of early human dispersal and migration route between southern and northern China. [ABSTRACT FROM AUTHOR]

Chinese loess is regarded as one of the most detailed and long-term archives of climate on land. However, there is still significant controversy over the deposit's origin, limiting interpretation of the sedimentological and paleoclimatic mechanisms responsible for its emplacement. Here this is addressed through morphology and the first laser ablation--inductively coupled plasma--mass spectrometer (LA-ICP-MS) U-Pb ages of detrital zircons from loess (last glacial age; northern Loess Plateau). These are compared to zircon U-Pb age spectra from desert and sandy lands surrounding the Loess Plateau. Surface samples were taken from the Tengger and Mu Us deserts, as well as the Horqin and Otindag sandy lands. The results demonstrate that zircon U-Pb ages can discriminate between potential source areas and highlight both similarities and differences in age spectra for the desert and sandy land samples. Most significantly, the loess age spectrum shows no single affinity to any of these regions and exhibits zircon ages associated with granitoid rocks representing tectonic events in both west and east northern China. Furthermore, and in contrast to proximal deserts, a significant proportion of zircons from the loess show affinities with rocks cropping out in the Qilian Mountains. The euhedral form of many of these grains further suggests direct transport from these crystalline source rocks, in contrast to previously hypothesized production or storage in deserts. Thus, dust-transporting storms tracked from the west during the last glacial maximum, although this does not explain all the zircon variability and implies multiple sources and storm-track variation over the depositional period. [ABSTRACT FROM AUTHOR]